It is well known in the prior art to use high compression ratio combustion chambers for internal combustion engines using a gasoline vapor fuel for stationary installations. These include four-stroke cycle internal combustion engines in which the fuel is injected directly into the air intake port of the combustion chamber or into the air induction manifold as well as engines that use a carburetted air/fuel supply. Research and development efforts in recent years have built upon earlier technology devoted to Otto cycle gasoline engines to improve the specific power output and to satisfy the recent emphasis placed on improving exhaust emissions and increasing fuel economy.
It is recognized that one of the ways to achieve improved fuel economy and to reduce undesirable exhaust emissions is to design the combustion chamber to achieve higher compression ratios while avoiding undesirable fuel pre-ignition in the cylinders. An attempt has been made in recent years also to improve engine operating efficiency by designing the engine to operate at leaner air/fuel ratios.
A high degree of fuel and air mixing is desirable because of its effect on engine performance. This characteristic usually is referred to as a homogeneous mixing of the combustible charge. It takes into account the gas dynamics, heat transfer and mass transfer that occurs during the induction process and during the combustion stages of the operating cycle.
The homogeneous nature of the combustible charge is affected by the timing of the opening of the inlet and exhaust valves during the combustion cycle, the presence of exhaust gas residuals and the mixing of the air and fuel in the combustion chamber, as well as the leanness of the air and fuel mixture.
Factors that affect the characteristics of the combustible mixture in the combustion chamber include the heat transfer that occurs between the cylinder walls and the combustible charge at the time of induction as well as at later stages in the combustion stroke. The combustion cycle is not truly adiabatic.
The parameters that affect the combustion and the combustion efficiency are the degree of advance of the spark timing and the characteristics of the flame front as well as the presence of pre-ignition reactions and so-called "hot spots" in the combustion chamber.
It also is known in the art that the generation of a pre-combustion by the spark of the ignition spark plug will generate a heat release that is greater than the heat loss to the surrounding gases at the initiation of combustion. The compression ratio and air/fuel ratio can be tailored to enable the so-called "hot nucleus" to both initiate and maintain combustion.
The delay between the timing of the spark and commencement of flame front propagation is affected by turbulence within the combustion chamber. Excessive turbulence, however, affects the initiation of the flame front because excessive turbulence can cause the flame front to be extinguished.
The effect of abnormal combustion also has long been recognized. It is generally acknowledged that this is due to the spontaneous ignition at several places within the unburned charge. That characteristic also is affected by the quality of the turbulence within the combustion chamber.
Compact combustion chambers have been used in some prior art designs. These include engines having compact combustion chambers located in the head of the cylinder or in the piston itself, and provision is made for obtaining a swirl of the intake gases at the time of entry of the charge into the reduced compact chamber volume.
Such homogeneous charge engines are distinguishable from so-called stratified charge engines, which are characterized by a rich mixture at the location on the spark plug and a leaner mixture elsewhere within the combustion chamber. This permits the engine to be operated at wide open throttle settings or at throttle settings near the wide open position, thus giving good fuel economy. This results, however, in low emission quality because the flame front may be extinguished, especially at light loads, before traversing the combustion chamber.
An example of a prior art four-cycle internal combustion engine in which provision is made for obtaining turbulence or a vortex in the combustion chamber is described in U.S. Pat. No. 4,000,722. That patent comprises an engine having a cylinder head that is equipped with a single inlet valve and a single outlet valve. Turbulence for the vortex normally is developed in a so-called swirl chamber within the cylinder. Typically, the height of the swirl chamber is less than its width, but the width is less than the total diameter of the combustion chamber so that the intake charge is characterized by a portion that has high turbulence and a separate portion that has a high surface-to-volume ratio.
A channel-type recess is formed in the cylinder head of the design of the '722 patent to facilitate the influx of fuel and air into a so-called swirl chamber, thus developing a rotational flow of the combustible gases. To facilitate the rotational flow or swirl, a guide channel extends in the direction of the rotation of the gas mixture within the cylinder. The height of the channel increases in the direction of the gas flow.
U.S. Pat. No. 4,329,955 shows a combustion chamber for an internal combustion engine wherein the exhaust valve is located at the center of two contiguous spherical chambers, each chamber having a swirl path which is adapted to sweep unburned gases from the combustion chamber during the combustion of the fuel, thereby improving engine performance. A separate spark plug is used to ignite gaseous fuel in each of the contiguous chambers.
U.S. Pat. No. 4,541,376 shows a four-stroke cycle engine having a deflector located in the intake gas flow path in the region of the swirl chamber so that swirl motion is broken into small-scale eddies by a spoiler device located in the combustion chamber. The introduction of turbulence is timed with the operation of the intake valve so that maximum turbulence will occur at the end of the compression stroke. The spark plug that initiates combustion is arranged in the cylinder head in a so-called quiescent zone near the spoiler device.
In the engine disclosed in U.S. Pat. No. 2,800,123, the intake valve and the exhaust valve are located in a common swirl chamber which is surrounded by a so-called squish zone. The majority of the gaseous charge, which is disposed around the spark plug located within the swirl chamber, will be burned rapidly. When the piston approaches the cylinder head, the large surface area of the squish zone will prevent premature burning of the charge, although the gases in that zone are compressed more rapidly than the gases in the remaining portions of the combustion chamber. Thus, the high velocity gases prior to ignition will flow into the high turbulence portion of the combustion chamber.
The spark plug is strategically located in the combustion zone, and the flame front, following ignition, will travel from the electrodes of the spark plug toward the more remote regions of the combustion chamber. Pre-ignition of the unburned gases in the region of the squish chamber as the flame front advances is discouraged because of the high heat transfer from the gases to the surrounding walls of the squish chamber. Although this may tend to reduce pre-ignition, it contributes to a high heat transfer between the gases and the surrounding wall and lowers thermal efficiency.
It also is known in the art to condition internal combustion engines of this type for operation with extra lean mixtures by providing a so-called torch device in the form of a pre-ignition auxiliary chamber that receives the air/fuel mixture at the time of the compression of the mixture and the mixture is ignited. That ignition tends to maintain combustion in the main portion of the combustion chamber, notwithstanding the presence of a lean air/fuel mixture. An attempt is made to increase the flame front propagation speed in the main combustion chamber by the torching effect of the flame turbulence in the auxiliary chamber, thereby improving the combustibility of the lean air/fuel mixture.
An example of such a pre-ignition chamber arrangement is described in U.S. Pat. No. 4,291,662, wherein a squish area establishes turbulence in a compact combustion chamber region and in a pre-combustion chamber. A spark plug is located at a point of communication between the two combustion chambers. A stable combustion condition is maintained using a lean air/fuel mixture in the auxiliary combustion chamber which establishes a burning jet or torch which is injected through the point at which the two combustion chambers are connected. The swirling motion of the air/fuel mixture in the combustion chamber is established by a so-called squish flow developed as the piston approaches top dead center and reduces the volume of the portion of the combustion chamber not occupied by the main compression chamber.
U.S. Pat. No. 4,331,115 has many of the characteristics described previously, including a swirl chamber, but the intake valve is located at the upper end of the swirl chamber so that entry of the combustible charge into the swirl chamber occurs as the intake passage establishes a tangential or swirling motion of the intake charge. The swirling motion is established by a channel-like connection between the area of the combustion chamber adjacent the exhaust valve and the main combustion chamber, thus establishing a tangential inflow of the charge that is compressed out of the squish area.
This vortex flow can be reinforced during the suction stroke as well as during the compression stroke.